The requirements in many data processing applications for storing relatively small amounts of information on removable and replaceable media have led to the development of disc drives incorporating inexpensive, flexible, removable magnetic recording discs. Exemplary of these disc drives is the Memorex Model 550, which accepts an industry standard removable recording disc contained within a protective envelope, the combination of the disc and envelope forming an easily handled recording disc cartridge such as that known in the trade as the Memorex Markette.TM. flexible disc cartridge. With these disc cartridges and drive units numerous different types of data may be stored, including program subroutines and diagnostic routines as well as process control data.
One of the highly desirable features of these relatively small and inexpensive storage devices is the ready removability and replaceability of the disc cartridges, thus providing for ready removability and replaceability of different data packages within the storage system. However, due to the thin and flexible nature of the disc recording media, one problem with these units has been that of protecting the disc cartridges against damage, particularly during insertion and removal of the cartridge from the disc drive unit. Frequently with prior art disc drive units the disc receiving structure, which receives a disc into the drive unit and then clamps it into engagement with a rotating spindle has been inadvertently closed with the disc less than fully inserted, thus often creasing or tearing the recording media and possibly destroying the usefulness of a disc cartridge so damaged. This problem has often arisen in prior art disc drives due to the absence of a positive indication of a full and proper insertion and registration of the disc cartridge therewithin and the absence of means for preventing improper closing and engagement of the disc cartridge when less than fully inserted. Similar problems have resulted from improper closing of access doors upon less than fully inserted discs, frequently also causing damage to the disc cartridge.